Even in the absence of an eruption, there are signs of activity at the summit of Mount Etna, Europe’s most active volcano. Water vapor and other volcanic gases overflow Etna’s summit craters, spilling out over the volcano’s upper slopes. A steam plume rises from a collapse pit that formed in late 2009, the newest volcanic feature on Etna. Dark lava flows from recent eruptions cover the peak, overlaying lighter, weathered flows from hundreds or thousands of years ago. (Numbers on the image indicate when a flow was erupted.) The oldest lavas are covered by green vegetation. Eruptive cones and fissures also dot the landscape.

Although Etna is not currently erupting lava or ash, there is more activity than just gas emissions. Frequent explosions deep within the Northeast Crater, which may presage an upcoming eruption, are audible at the summit. These explosions were occurring sporadically every few minutes, as recorded by nearby seismometers.